Method for rendering cellulosic materials fire resistant with phosphorous oxychloride-anhydrous ammonia reaction products and products produced thereby



Patented Dec. 1, 1953 UNITED STATES OFFICE Russell L. Jenkins, Anniston, Ala-., assi'gnor t Monsanto Chemical Company, St. Louis, Me, a

corporation of Delaware No Drawing. Application J one 21,1950, Se'lial No. 169,506

2 Claims.

The present invention relates to the treatment of cellulosic materials in order to improve their resistance to fire.

It is an object of the invention to provide a process for rendering cellulosic materials fireresistant. It is another object of the invention to provide flame-resistant cellulosic products. Still another object of the invention is the modification of textile fibers and other combustible materials containing cellulose to render the same resistant to fire.

It is known in the prior art that cellulosic materials such as textile product can be modified to improve their resistance to fire by treatment with phosphorus compounds. For example, U. S. Patent 2,401,440 describes the treatment of cellulosic products such as alkalized cellulose by treatment first with phosphorus oxychloride and then with ammonia, while the products produced by the process described in this patent contain chemically bound phosphonamide groups, the treatment involved the use of chemical reagents which the textile processing industry Was not generally equipped to handle. For this reason a simpler method which could be used in the ordinary textile plant without special equipment or skills was greatly tobe desired.

In accordance with the terminology which has been developed in this field fire-resistance and flame-resistance result from the treatment of a material such as cloth with variou chemicals so that it becomes resistant to the propagation of flame across its surface after the igniting flame has been removed; that is, a flame-resistant material willjnot support combustion independently of an external source of heat. In contact with an open flame, however, or at elevated temperatures, flame-resistant cellulosic material can be expected to char and decompose.

The products of the present invention exhibit the properties of fire-retardancy while at the same time maintaining to a large degree the original hand of the material. The color, physical appearance and tensile strength are not substantially afiected by the present treatment.

It has been found that the treatment of combustible cellulosic materials, such as cotton and other cellulosic derivatives such as rayon, with the water-soluble, nitrogenand phosphoruscontaining product described in copending application Serial No. 169,513, filed June 21, 1950, which application is assigned tothe same assignee as is the present case results in the production of a permanent flame-resistant product of excellent hand, which exhibits substantially the strength of the untreated fabric.

According to the copending application re-- ferred to above, the nitrogenand phosphorus-- containing products utilized in the present in vention are produced by reacting together phosphorus oxychloride and ammonia at tempera= tures below C., preferably in an inert solvent. The product produced by the said reaction is then heated to a temperature of at least C., but not above C. The above reao tion results in the formation of by-product am monium chloride corresponding in amount to the chlorine present in the phosphorus oxychloride. For the present purpose the ammonium chloride should be largely removed. This is done by the extraction of the heat-treated phosphorus oxychloride-ammonia reaction product by means of solvents. In general, the extraction is best carried out employing liquid anhydrous ammonia as the extracting solvent, which dissolve the ammonium chloride preferentially leaving the nitrogen-phosphorus compound as a white, non-hygroscopic solid.

In carrying out the process 'of the invention to produce the present products, the preparation may suitably commence with the solution of phosphorus oxychloride in a solvent. The phosphorus oxychloride so dissolved is then reacted with ammonia in gaseous or liquid form with suitable agitation. The temperature should be maintained below 100 C. during the addition of the ammonia. However, after the addition of at least the stoichiometric proportion of ammonia (5 moles per mole of POClz) the temperature is raised and theproduct heated to at least 110C, but not abovel50 C. It has been found that the temperature control within the above limits is essential to prevent the formation of a water-insoluble product on the one hand, and on the other hand to alter the intermediate product so that the subsequent separation and purification steps can be carried out successfully. The reaction of phosphorus oxychloride with ammonia, followed by heating the reaction product to at least 110' C., but not above 150 0., yields the desired composition in a form insoluble in liquid anhydrous ammonia. formed as a by-product by reaction of ammonia with the chloride present in the phosphorus oxychloride. As a result of the conditions under which the present product is prepared, it has been found to be possible to form the nitrogenphosphorus product so that it possessessolubility characteristics enabling the subsequent separation of the product from the ammonium chloride to be carried out by differential solubility methods. .At the same time the desired product is ob- Ammonium chloride is.

tained in a form which is highly reactive with cellulose.

Preferred solvents for carrying out the production of the initial condensation product of ammonia with phosphorus oxychloride are any inert liquid, such as kerosene, naphtha, hexane, benzene, acetone, or other organic liquids which do not react with ammonia or phosphorus oxychloride.

Phosphorus oxychloride to the amount of 90 pounds is dissolved in 90 gallons of hexane contained in an autoclave. The solution is heated to approximately 55 C. while stirring, and gaseous anhydrous ammonia is added thereto. Although an exothermic reaction takes place, the reaction may be carried. out at about 75 C. by cooling the vessel. Ammonia to the extent of 50 pounds (5 moles per mole of phosphorus oxychloride) is added to the autoclave over a two hour period. An excess of ammonia may be used. After the addition of this amount of ammonia, the autoclave is sealed and then heated to about 130 C. for approximately 1. /2 hours. After the completion of the heating period, the reaction mixture is cooled to below 40 C. and then transferred to a second vessel containing a filter element and provided with external heating means. By applying heat to the autoclave contents the hexane present is distilled ofi, condensed and recovered. The remaining solids which consist of a mixture of the nitrogenand phosphorus-centaining product with ammonium chloride are then extracted under pressure with anhydrous ammonia at about room temperature. A total of about pounds of ammonia per pound of final product is employed, although it is also possible to carry out an extraction with 10 pounds of ammonia per pound of product. The slurry of product in anhydrous liquid ammonia was filtered by means of a filtering device contained within the autoclave. In this manner, substantially all of the ammonium chloride is leached from the residual solids. After the last extraction the residual ammonia adhering to the product is removed by evaporation induced by the application of heat to the product. The yield of the nitrogen-phosphorus product obtained is approximately 85% of the theoretical. The product contains 33.8% nitrogen, 35.1% phosphorus, N/P ratio=2.l4. This is an atomic ratio.

The nitrogen-phosphorus product so produced has, when dissolved in aqueous solutions, a pH within the range of from 7.0 to 8.5, a molecular weight of from 180 to 300, a preferred range being 200 to 250, and having a nitrogen to phosphorus atomic ratio of from 2.1 to 2.3, the latter ratio depending somewhat upon the temperature employed in the heating step. The so-formed nitrogen-phosphorus product is soluble not only in water, but also in glyoerine, ethylene glycol, and formamide.

Cellulosic textile products are impregnated or coated with the above-described nitrogen-phosphorus-containing product by immersing said textile materials in solutions thereof. Aqueous solutions are preferred, but other solvents may also be used. The concentration of the solutions may vary over a wide range, depending upon the desired add-on which is to be obtained. It is generally desirable for the present purpose to add from 8% to by weight of the phosphorus-nitrogen-containing product to the textile fabric, although a range of 2% to 90% may be employed, such as in applications where creaseor crush-resistance is desired. In the treatment of rayon it has also been found that dimensional stabilization is greatly improved as a result of the deposition of the nitrogen-phosphorus composition.

After impregnation of the textile fabric and in order to produce a wash-fast fabric, the impregnated fabric is dried and then subjected to a temperature of at least but below 200 C. If it is not necessary to produce a wash-fast product the heating step may be omitted.

The following examples illustrate this invention:

EXAMPLE 1 Filter paper was impregnated at room tempera.- ture with a 20% solution of the nitrogen-phosphorus product. After drying at room temperature the impregnated paper was cured by heating at 150 C. for 10 minutes. The treated paper was found to be flame-resistant.

The details of the testing procedure utilized for determining the flame-resistant qualities of the present products were carried out in accordance with the methods described in the Paper Trade Journal, vol. 117, No. 12, page 28.

The treated paper showed substantially no change in color, and upon exposure to warm, moist air did not reveal any evidence of hygroscopicity. The sample exposed to high humidity, followed by drying, retained its flameproofing quality.

EXAMPLE 2 A piece of cotton cloth was treated with a 40% aqueous solution of the nitrogen-phosphorus product. After drying and curing at 150 C. for 10 minutes, the cloth was washed at for 30 minutes. An add-on of 26.5% remained, and analysis of the treated cloth showed the presence thereof of 6% phosphorus. The flame-resistance remained after two laundry-type washes at 180 F. Another sample was washed 20 times under conventional home laundering conditions, also retaining the flame-resistance property.

The details of the testing procedure utilized for determining the fire-resistance qualities of the present products were carried out in accordance with the methods described in R. W. Little, Flameproofing Fabric Materials (Reinhold Publishing Co., 1947) EXAMPLE 3 An aqueous solution containing 18% of the nitrogen-phosphorus product was applied to a cotton fabric in a padder in such a manner as to give 85% wet pick up. The fabric was dried at 110 C. and then heated at a temperature of C., for five minutes. The product so obtained showed a loss of less than 10% of the original tensile strength of the fabric, was completely fire-resistant and moreover showed no evidence of glow after extinction of the flame. The product was subjected to 50 successive washes without loss of its original fire-retardancy.

The above process is applicable to textile products over a wide variety of solution concentrations. For example, aqueous solutions containing from 2.5% to 60% of the nitrogen-phosphorus-containing product may be employed. Moreover, drying of the impregnated fabric may be carried out without the application of heat. However, subsequent heat treatment or curing should be carried out at least at temperatures above 100 C., but preferably not in excess of 200 C.

In the application of the nitrogen-phosphorus compound to cellulosic materials to render them fire-resistant, it is also contemplated that other chemical compositions may be used in combination therewith. For example, other fire-retardant compositions such as antimony oxide may be applied, either as a separate operation, or simultaneously. In such a treatment, the nitrogen-phosphorus composition is of particular utility in repressing the catalyst tendency of the metal oxides which would exhibit after-glow for a long period unless the nitrogen-phosphorus compound is present.

Further characterization of the products of the present invention, and an indication of the reactivity with cellulose is afiorded by application of the test procedure, described by F. V. Davis et al. in the Journal of the Textile Institute, 40, pages T 839-T 854 (1949).

For the present purpose the method of Davis et al. was modified in such a manner as to increase the criticality of the reactivity test. The modification consisted in washing the treated fabric with a synthetic detergent solution at 120 followed by a cycle of three rinses, also conducted at 120 1 h, rather than by conducting the entire washing in distilled water. The degree of reactivity was then obtained by drying the impregnated cotton fabric at 220 F., and weighing the fabric samples to determine the amount of the nitrogen-phosphorus product remaining, which, it may be assumed, had combined chemically with the cellulose oi the fabric.

The test utilized to determine the cellulose reactivity of the present and related products is carried out by contacting a standard sample of desized cotton, of sheeting weight, with an aqueous solution containing 6% by weight of solids of the present nitrogen-phosphorus compound. The cotton is allowed to take up about 100% of its weight of the solution, after which the impregnated sample is dried and then cured by heating for 10 minutes at 150 C. The sample is then washed at 120 F. in a synthetic detergentcontaining solution, which washing is then followed by three standard rinses with water also carried out at 120 After washing and rinsing, as described above, followed by drying to constant weight, the sample is weighed and the add-on thus determined. The amount of nitrogen-phosphorus compound retained by the washed sample in comparison with the amount retained on an unwashed sampl is a measure of the amount of the product adhering to the fabric by reason of its chemical activity therewith. The relative amounts can be expressed in percent. As a result of this test, the present nitrogenphosphorus compound is found to possess a reactivity of 80-90%, which means that 80-90% of the nitrogen-phosphorus compound applied to the cellulose has combined chemically therewith. In comparison with the present product the higher molecular weight, water-insoluble produots which are described in application Serial No. 68,402, filed December 30, 1948, now U. S. Patent 2,596,935, applied by means of an aqueous dispersion, have a reactivity of approximately The above reactivity test may also be employed to evaluate the cellulose reactivity of other prior art materials such, for example, as guanidine phosphate, which material was found by this test to have a reactivity with cellulose of 31%.

The table below summarizes the cellulose reactivity of the several phosphorus compounds mentioned above and includes in addition several other products. The data obtained with the 6 urea-diammonium phosphorus composition were taken from the book by R. W. Little; Flameproofing of Textile Fabrics.

causing fiber loss).

What I claim is:

1. A process for the treatment of cellulosic textiles which comprises impregnating the said cellulosic textiles with a previously-prepared solution of a nitrogenand phosphorus-containing product, to apply to the said textiles from 2% to by weight of the said nitrogenand phosphorus-containing product, and thereafter drying the said impregnated cellulosic material, said nitrogenand phosphorus-containing product being obtained by reacting one mole of phosphorus oxychloride with at least five moles of anhydrous ammonia in an inert solvent, which dissolves but does not react with the said reactants, at a temperature below C. to produce an initiallyformed, anhydrous-ammonia-soluble product mixed with ammonium chloride, thenheatingsaid initially-formed nitrogenand phosphoruscontaining product to a temperature of at least C. but below C. until said nitrogenand phosphorus-containing product is rendered substantially insoluble in liquid anhydrous ammonia, and has a molecular weight within the limits of from to 300, a nitrogen/phosphorus atomic ratio within the limits of from 2.1 to 2.3, and when dissolved as a saturated solution in water yields a solution having a pH within the limits of 7.0 to 8.5.

2. A glow-resistant cellulose textile containing 2% to 90% by weight of a nitrogenand phosphorus-containing product obtained by reacting one mole of phosphorus oxychloride with at least five moles of anhydrous ammonia in an inert solvent, which dissolves but does not react with the said reactants, at a, temperature below 100 C. to produce an initially-formed, anhydrousammonia-soluble product mixed with ammonium chloride, then heating said initially-formed nitrogenand phosphorus-containing product to a temperature of at least 110 C. but below 150 C. until said nitrogenand phosphorus-containing product is rendered substantially insoluble in liquid anhydrous ammonia, has a molecular weight within the limits of from 180 to 300, a nitrogen/phosphorus atomic ratio within the limits of from 2.1 to 2.3, and when dissolved as a saturated solution in water yields a solution having a pH within the limits of 7.0 to 8.5.

RUSSELL L. JENKINS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,052,886 Leroy Sept. 1, 1936 2,163,085 Cupery June 20, 1939 2,401,440 Thomas et al June 4, 1946 OTHER REFERENCES Mellor, Comprehensive Treatise of Theoretical Inorganic Chemistry, volue 8, page 707 (1928). 

1. A PROCESS FOR THE TREATMENT OF CELLULOSIC TEXTILES WHICH COMPRISES IMPREGNATING THE SAID CELLULOSIC TEXTILES WITH A PREVIOUSLY-PREPARED SOLUTION OF A NITROGEN-AND PHOSPHORUS-CONTAINING PRODUCT, TO APPLY TO THE SAID TEXTILES FROM 2% TO 90% BY WEIGHT OF THE SAID NITROGEN-AND PHOSPHORUS-CONTAINING PRODUCT, AND THEREAFTER DRYING THE SAID IMPREGNATED CELLULOSIC MATERIAL, SAID NITROGEN-AND PHOSPHORUS-CONTAINING PRODUCT BEING OBTAINED BY REACTING ONE MOLE OF PHOSPHORUS OXYCHLORIDE WITH AT LEAST FIVE MOLES OF ANHYDROUS AMMONIA IN AN INERT SOLVENT, WHICH DISSOLVES BUT DOES NOT REACT WITH THE SAID REACTANTS, AT A TEMPERATURE BELOW 100* C. TO PRODUCE AN INITIALLYFORMED, ANHYDROUS-AMMONIA-SOLUBLE PRODUCT MIXED WITH AMMONIUM CHLORIDE THEN HEATING SAID INITIALLY-FORMED NITROGEN-AND PHOSPHORUS-CONTAINING PRODUCT TO A TEMPERATURE OF AT LEAST 110* C. BUT BELOW 150* C. UNTIL SAID NITROGEN-AND PHOSPHORUS-CONTAINING PRODUCT IS RENDERED SUBSTANTIALLY INSOLUBLE IN LIQUID ANHYDROUS AMMONIA, AND HAS A MOLECULAR WEIGHT WITHIN THE LIMITS OF FROM 180 TO 300, A NITROGEN/PHOSPHORUS ATOMIC RATIO WITHIN THE LIMITS OF FROM 2.1 TO 2.3, AND WHEN DISSOLVED AS A SATURATED SOLUTION IN WATER YIELDS A SOLUTION HAVING A PH WITHIN THE LIMITS OF 7.0 TO 8.5. 